For A4 size document use following dimension
var pgSize = new iTextSharp.text.Rectangle(600f, 700f);
Document doc = new Document(pgSize, 1.5f, 1.5f, 1f, 0.5f);
BaseFont bf = BaseFont.CreateFont("c:\\\\windows\\\\fonts\\\\calibri.ttf", BaseFont.IDENTITY_H, false);